We are attempting to define the genetic basis of cell-cell recognition. As a first step, we plan to characterize the genes encoding the major histo-compatibility antigens (transplantation antigens) and the Ia antigens (immune associated antigens) by the use of recombinant DNA technology. Our initial efforts have been directed towards obtaining cloned cDNAs corresponding to these genes. During the past year we have obtained cDNA clones for murine beta-2 microglobulin mRNA and H-2 mRNA and we have begun to search for I-A cDNA clones. The structure, evolution, and expression of the single murine beta-2 microglobulin gene and the multiple H-2-like genes are being studied with the aid of the cloned cDNAs.